Embodiments of the invention relate generally to structures and methods for packaging light emitting semiconductor devices and, more particularly, to a flexible overlay circuit structure for interconnecting light emitting semiconductor devices.
Power semiconductor devices are semiconductor devices used as switches or rectifiers in power electronic circuits, such as switched mode power supplies, for example. Most power semiconductor devices are only used in commutation mode (i.e., they are either on or off), and are therefore optimized for this. One such device is a semiconductor light emitting device, with a prominent example being a light emitting diode (LED). LEDs are semiconductor chips that are packaged to emit radiation in response to an applied voltage or current. These LEDs are used in a number of commercial applications such as automotive, display, safety/emergency, and directed area lighting. LEDs may be fabricated using any materials which emit visible, ultra-violet, or infrared radiation. Currently, LEDs are typically assembled onto insulated metal substrates. The insulated metal substrates (IMS) include a metal baseplate (e.g., aluminum baseplate) covered by a thin layer of dielectric material (e.g., an epoxy-based layer) and a layer of copper, with the baseplate then being attached to a heatsink to provide cooling. One face of the LED chip/die is then typically soldered or silver adhesive attached to the IMS copper and the other terminal/face wirebonded to the IMS. Alternatively, the LED chip can be packaged in a first level package which can then be soldered to the IMS. In this first level package, one face of the LED chip is soldered or silver die attached to a pad on a substrate (metalized ceramic or polymer) and the other terminal/face is attached via wirebond to another pad on the same substrate. This first package may optionally include heat slugs.
It is recognized, however, that there are several drawbacks to the existing method of assembling arrays of LEDs on an IMS and of the wirebonding of the LED chips/dies to the IMS. For example, it is known that LEDs may be fabricated for use in a variety of products that have a curved surface or shape, including lighting products such as round lamp bulbs, flood lights, cylindrical flashlights, etc. In such products, it can be difficult to wirebond the LED chips/dies to a curved surface IMS. As another example, it is recognized that the form factor of the IMS limits applications or implementations of an array of LEDs to use only as a directional light source, when it may be desirable for the array of LEDs to be applied or implemented in more complex shapes, such as shapes typical in general incandescent lighting. As yet another example, it is recognized that layer of dielectric material in the IMS can add unnecessary thermal resistance that may negatively impact the performance and/or efficiency of the array of LEDs.
Accordingly, it is desirable to provide a semiconductor light emitting device package that is freed from the constraints and drawbacks associated with mounting on a standard IMS. It is further desirable for such a semiconductor light emitting device package to be adaptable and conformable to a plurality of complex shapes and eliminate the limitations associated with wirebonds.